An X-ray CT scanner is configured to reconstruct a tomographic image based on the projection data obtained by causing an X-ray source to irradiate an object with X-rays, while rotating an X-ray source around the body axis of the object, and causing an X-ray detector to detect the X-rays transmitted through the object. The X-ray CT scanner plays an important role in medical activities including disease diagnosis, medical treatment, and surgery planning.
In general, the X-ray CT scanner reconstructs an image, assuming that the locus of an X-ray focus is a true circle. For this reason, the vibration caused when the gantry on which the X-ray source and X-ray detector are mounted rotates becomes the direct cause of a deterioration in the image quality of a reconstructed image, and particularly the spatial resolution.
Conventionally, in consideration of this fact, attempts have been made to suppress vibration by measuring gantry vibration at the time of rotation and adjusting the installed states of the respective units on the gantry so as to reduce the measured value.
As a method of measuring gantry vibration, there is used a method of directly or indirectly measuring the displacement of each mechanism included in the gantry. As a typical method, there is available a method of measuring the displacement of each unit on the gantry while actually rotating the gantry.
However, there are various problems in such a conventional measurement method.
For example, even when a vibration value as a measurement result is very small, if the frequency of the vibration value is high, a noticeable artifact may occur in a reconstructed image. In contrast, even when a vibration value as a measurement result is large, if the frequency of the vibration value is low, the influence of the vibration on image quality may be negligibly small. As described above, the measurement result on gantry vibration and the influence of the vibration on image quality do not always have a one-to-one relationship.
In addition, since it is necessary to measure the vibration values of the respective measurement target portions in various directions, large equipment is required for measurement.
Under the circumstances, it is necessary to provide some means for facilitating specifying the degree of influence of gantry vibration on a reconstructed image and the cause of gantry vibration.